1. Field of the Invention
The present invention relates to an image generating apparatus comprising a take-up reel taking up an ink sheet on a take-up bobbin.
2. Description of the Background Art
A torque limiter mechanism applied to an image generating apparatus or the like comprising a take-up reel taking up an ink sheet on a take-up bobbin is known in general, as disclosed in each of Japanese Patent Laying-Open Nos. 2005-344858, 7-269589 (1995), 5-106641 (1993), 7-229524 (1995) and 2005-199520, for example.
The aforementioned Japanese Patent Laying-Open No. 2005-344858 discloses a torque limiter comprising a rotating cylindrical housing and an inner race including a plurality of torque limiting members integrally having deflectable elastic portions annularly provided on the outer peripheral surface thereof. In the torque limiter described in Japanese Patent Laying-Open No. 2005-344858, the torque limiting members of the inner race fitted with the inner peripheral surface of the housing coaxially with the housing slidably come into contact with the inner peripheral surface of the housing while applying prescribed pressing force in a direction expanding the inner diameter.
The aforementioned Japanese Patent Laying-Open No. 7-269589 discloses a torque limiter constituted of a power output member including a flange portion having a first end surface annularly provided with a plurality of deflectable engaging portions at a constant interval and a second end surface connectable with an output shaft, a power input member including a flange portion having a first end surface connectable with a driving shaft of a driving source and a friction member wound on and fixed to the outer peripheral surface of a small-diametral portion axially extending from a second end surface of the flange portion and a torsion coil spring fitted with the outer peripheral surfaces of the engaging portions of the power output member as well as a paper feeder and an office machine each employing this torque limiter. In the torque limiter as well as the paper feeder and the office machine each employing this torque limiter described in Japanese Patent Laying-Open No. 7-269589, the small-diametral portion of the power input member and the outer peripheral surfaces of the engaging portions of the power output member are fitted with each other through the friction member while the outer peripheral surfaces of the engaging portions of the power output member are clamped by the torsion coil spring toward the axial center, to slidably come into contact with the friction member fixed to the small-diametral portion of the power input member while applying prescribed pressing force.
The aforementioned Japanese Patent Laying-Open No. 5-106641 discloses a torque limiter comprising a rotating cylindrical outer race, a cylindrical inner race rotatable inside the outer race and a coil spring fitted between the inner and outer races and integrally provided with a large-diametral coil portion and a small-diametral coil portion. In the torque limiter described in Japanese Patent Laying-Open No. 5-106641, the large-diametral coil portion of the coil spring fitted with the inner peripheral surface of the outer race slidably comes into contact with the inner peripheral surface of the outer race while applying prescribed pressing force to the inner peripheral surface of the outer race in a direction expanding the inner diameter while the small-diametral coil portion of the coil spring fitted with the outer peripheral surface of the inner race slidably comes into contact with the outer peripheral surface of the inner race while applying prescribed pressing force to the outer peripheral surface of the inner race in a direction reducing the outer diameter.
The aforementioned Japanese Patent Laying-Open No. 7-229524 discloses a bidirectional torque limiter comprising a rotating cylindrical outer tube, a cylindrical inner tube provided with a spring storage portion and rotatable inside the outer tube and a coil spring fitted between the inner and outer tubes and integrally provided with clockwise and counterclockwise coil portions linked with each other. In the bidirectional torque limiter described in Japanese Patent Laying-Open No. 7-229524, the counterclockwise coil portion of the coil spring fitted with the inner peripheral surface of the outer tube slidably comes into contact with the inner peripheral surface of the outer tube while applying prescribed pressing force to the inner peripheral surface of the outer tube in a direction for expanding the inner diameter while the clockwise coil portion of the coil spring fitted with the spring storage portion of the inner tube slidably comes into contact with the spring storage portion of the inner tube while applying prescribed pressing force to the inner peripheral surface of the spring storage portion of the inner tube in a direction for expanding the inner diameter.
The aforementioned Japanese Patent Laying-Open No. 2005-199520 discloses a ribbon take-up mechanism (torque limiter mechanism) constituted of a cylindrical bobbin gear provided with a gear portion on a prescribed position of the outer periphery thereof, a bobbin shaft mounted with a take-up bobbin and a close-coiled spring fitted with the outer peripheral surface of a shaft portion of the bobbin gear. In the ribbon take-up mechanism (torque limiter mechanism) described in Japanese Patent Laying-Open No. 2005-199520, the close-coiled spring clamps the outer peripheral surface of the shaft portion of the bobbin gear toward the center of the rotation axis, thereby providing prescribed clamping force to the bobbin shaft slidably coming into contact with the inner peripheral surface of the shaft portion of the bobbin gear.
In the conventional torque limiter proposed in the aforementioned Japanese Patent Laying-Open No. 2005-344858, however, the torque limiting members regularly generating the pressing force toward the inner peripheral surface of the housing are integrally formed on the inner race. Depending on the material of the inner race, therefore, the elastic portions of the torque limiting members may conceivably be so aged with time that the pressing force cannot be kept constant. In this case, slip torque set in manufacturing cannot be maintained, whereby torque control cannot be precisely performed. When the torque limiter according to Japanese Patent Laying-Open No. 2005-344858 is applied to a take-up reel of an image generating apparatus comprising a driving source transporting an ink sheet of an ink sheet cartridge and the take-up reel transmitting the driving force of the driving source to a take-up bobbin of the ink sheet cartridge and taking up the ink sheet on the take-up bobbin, therefore, the take-up reel cannot perform proper torque control on the take-up bobbin upon action of the torque limiter function.
In the conventional torque limiter proposed in the aforementioned Japanese Patent Laying-Open No. 7-269589, the power output member and the power input member must be arranged inside the torsion coil spring, in order to utilize clamping force of the torsion coil spring reducing the coil diameter. Therefore, the power output member and the power input member are in contact with each other through the friction member on positions close to the rotation axes thereof, whereby the contact regions are reduced particularly in the circumferential direction. Thus, the torsion coil spring must apply limited clamping force to the small contact regions, whereby it is conceivably difficult for the torque limiter to stably operate. When the torque limiter according to Japanese Patent Laying-Open No. 7-269589 is applied to the take-up reel of the image generating apparatus comprising the driving source transporting the ink sheet of the ink sheet cartridge and the take-up reel transmitting the driving force of the driving source to the take-up bobbin of the ink sheet cartridge and taking up the ink sheet on the take-up bobbin, therefore, the ink sheet cannot be stably taken up on the take-up bobbin with proper tensile force.
In the conventional torque limiter proposed in the aforementioned Japanese Patent Laying-Open No. 5-106641, the large- and small-diametral coil portions of the coil spring in contact with the inner peripheral surface of the outer race and the outer peripheral surface of the inner race respectively themselves directly perform sliding operations (rotating operations) upon action of the torque limiter function. Therefore, the coil spring conceivably generates heat due to friction and stops this heat generation upon nonaction of the torque limiter function. Consequently, the elastic force of the coil spring is conceivably aged with time due to repetitive heat generation and cooling. In this case, slip torque set in manufacturing cannot be maintained, whereby torque control cannot be precisely performed. When the torque limiter according to Japanese Patent Laying-Open No. 5-106641 is applied to the take-up reel of the image generating apparatus comprising the driving source transporting the ink sheet of the ink sheet cartridge and the take-up reel transmitting the driving force of the driving source to the take-up bobbin of the ink sheet cartridge and taking up the ink sheet on the take-up bobbin, therefore, the take-up reel cannot perform proper torque control on the take-up bobbin upon action of the torque limiter function.
In the conventional bidirectional torque limiter proposed in the aforementioned Japanese Patent Laying-Open No. 7-229524, the clockwise and counterclockwise coil portions of the coil spring in contact with the inner peripheral surface of the outer tube and the spring storage portion of the inner tube respectively themselves perform sliding operations (rotating operations) upon action of the torque limiter function. Therefore, the coil spring conceivably generates heat due to friction and stops this heat generation upon nonaction of the torque limiter function. Consequently, the elastic force of the coil spring is conceivably aged with time due to repetitive heat generation and cooling. In this case, slip torque set in manufacturing cannot be maintained, whereby torque control cannot be precisely performed. When the bidirectional torque limiter described in Japanese Patent Laying-Open No. 7-229524 is applied to a take-up reel of an image generating apparatus comprising a driving source transporting an ink sheet of an ink sheet cartridge and the take-up reel transmitting the driving force of the driving source to a take-up bobbin of the ink sheet cartridge and taking up the ink sheet on the take-up bobbin, therefore, the take-up reel cannot perform proper torque control on the take-up bobbin upon action of the torque limiter function, similarly to the case of the torque limiter described in Japanese Patent Laying-Open No. 5-106641.
In the conventional ribbon take-up mechanism proposed in the aforementioned Japanese Patent Laying-Open No. 2005-199520, the shaft portion of the bobbin gear and the bobbin shaft must be arranged inside the close-coiled spring, in order to utilize clamping force of the close-coiled spring reducing the coil diameter. Therefore, the shaft portion of the bobbin gear and the bobbin shaft are in contact with each other on positions close to the rotation axes thereof, whereby the contact regions are reduced particularly in the circumferential direction. Thus, the close-coiled spring must apply limited clamping force to the small contact regions, whereby it is conceivably difficult for the ribbon take-up mechanism to stably operate. When the ribbon take-up mechanism according to Japanese Patent Laying-Open No. 2005-199520 is applied to a take-up reel of an image generating apparatus comprising a driving source transporting an ink sheet of an ink sheet cartridge and the take-up reel transmitting the driving force of the driving source to a take-up bobbin of the ink sheet cartridge and taking up the ink sheet on the take-up bobbin, therefore, the ink sheet cannot be stably taken up on the take-up bobbin with proper tensile force, similarly to the case of the torque limiter described in Japanese Patent Laying-Open No. 7-269589.